Two important monooxygenase enzymes, dopamine-b-hydroxylase (DBH) and peptidylglycine hydroxylating monooxygenase (PHM) are involved in the biosynthesis of neurotransmitters and peptide hormones, and are thus of pivotal importance in cell signalling mechanisms, and neuroregulatory function. The research is focussed toward elucidating the coordination chemistry of the Cu(I) forms of the enzymes, at which dioxygen-binding and substrate hydroxylation occur. Novel methodologies involving binding of Cu(I)-specific ligands such as CO and isocyanides will be developed as powerful probes of Cu(I) structure and substitution chemistry. Site directed mutants of PHM will also be studied in order to test current models of active-site structure.